The present invention relates to magnetic heads, and magnetic storage apparatus using the same. More particularly, the invention relates to a magnetic storage apparatus which comprises a magnetic head including a single pole type writer, and a double layered magnetic recording medium having a soft magnetic under layer.
To enhance recording density of a magnetic disk device, a double layered perpendicular recording system is advantageous which combines a double layered perpendicular magnetic recording medium having a recording layer and a soft magnetic under layer, and a magnetic head having a single pole type writer mounted thereon. FIG. 13 is a schematic diagram illustrating the structure of the magnetic head and the medium in the double layered perpendicular recording system. The single pole type writer includes a main-pole 11, a return-pole 12, and a coil 13 for generating recording magnetic fields to be applied to a double layered perpendicular magnetic recording medium 20 by the main-pole 11. The single pole type magnetic head is generally formed integrally with a read head which includes a magneto-resistive element sandwiched between a pair of reader shields 14 and 15. The double layered perpendicular magnetic recording medium 20 comprises a soft magnetic under layer 22, a magnetic recording layer 23, and a protective layer 24, which are formed on a substrate 21. Between the magnetic recording layer and the soft magnetic under layer, or between the soft magnetic under layer and the substrate, a non-magnetic layer may intervene for the purpose of, for example, improvement of crystallinity of an upper layer, improvement of interlaminar adhesion, or the like. It should be noted that there is proposed an application of the single pole type recording head which includes a soft magnetic member disposed in the vicinity of a main-pole so as to change recording field distribution, but a magnetic pole that generates a magnetic field to finally magnetize the recording medium is herein defined as a main-pole.
FIG. 14 shows explanatory diagrams of a double layered perpendicular recording system and a longitudinal recording system. More specifically, FIG. 14(a) shows the double layered perpendicular recording system, while FIG. 14(b) the longitudinal recording system. As shown in the FIG. 14(b), in the conventional longitudinal recording system, a magnetic field 142 leaking from a recording head gap 141 is used to record information on a medium 143. On the other hand, in the use of a double layered perpendicular recording medium, since a magnetic flux created from a recording element passes through a soft magnetic under layer 22, the recording field density 143 144 to be applied to the magnetic recording layer 23 becomes large. This feature of the double layered system is an advantage in the achievement of high density. However, in this system, when an external field is applied from the outside as shown in FIG. 15, magnetic fluxes are concentrated between the magnetic head and the soft magnetic under layer, thus causing extremely large magnetic fields directly below the main-pole 11 of the magnetic head, compared with magnetic fields 151 applied from the outside. Such concentration of stray magnetic fields on the magnetic head erases recorded data or degrades the quality of signals. A remedial measure against this problem may be provided by the modification of the structure and magnetic characteristics of the head, and of the structure and magnetic characteristics of the soft magnetic under layer. However, it is inevitable in view of the principle that the double layered perpendicular recording system is more sensitive to the external field than the conventional longitudinal magnetic recording system.
To avoid this problem, hitherto, there is proposed a system which includes a soft magnetic shield attached to the whole or part of the device. In any case, the device has an object to decrease the amount of the magnetic fluxes flowing in the head of the device and the recording medium by attaching the shield serving as a composition other than the head and the medium so as to divert the magnetic fluxes created by the external field through the shield.
Known systems are described, for example, in JP-A No. 47110/2004, JP-A No. 77266/2003, and JP-A No. 236674/1994.